php计算执行时间的类(计算函数或代码的执行时间)

<?php
class c_Timer {
var $t_start = 0;
var $t_stop = 0;
var $t_elapsed = 0;
function start() {
$this->t_start = microtime();
}
function stop() {
$this->t_stop = microtime();
}
function elapsed() {
if ($this->t_elapsed) {
 return $this->t_elapsed;
} else {
 $start_u = substr($this->t_start,0,10);
 $start_s = substr($this->t_start,11,10);
 $stop_u = substr($this->t_stop,0,10);
 $stop_s = substr($this->t_stop,11,10);
 $start_total = doubleval($start_u) + $start_s;
 $stop_total = doubleval($stop_u) + $stop_s;
 $this->t_elapsed = $stop_total - $start_total;
 return $this->t_elapsed;
}
 }
};
?>

<?php
$timer = new c_Timer;
$timer->start();
echo "<hr>";
$timer->stop();
echo $timer->elapsed();
?>